This invention pertains to oscillator circuits generally referred to as solid state microwave oscillators, and more particularly, to oscillator circuits using negative impedance semiconductor devices. A negative impedance oscillator basically comprises a negative impedance device connected through a resonator, tuned to the desired frequency, to a load. The impedance presented by the cavity and load to the device is the complex conjugate of the negative impedance device. Typical examples of negative impedance devices used for generating microwave oscillations are the transistor, IMPATT diode, GUNN-Effect diode, tunnel diode and LSA diode, etc. With the possible exception of the GUNN effect diode, these devices all require that energy be fed back to the input terminals in sychronism with the RF voltage across the diode to maintain continuous oscillation. Unfortunately, even when design precautions are taken, frequencies other than the desired frequency may be generated causing frequency instability.
Prior art microwave oscillators, generally have a low Q, moding or oscillations at frequencies other than the one desired, and/or power loss due to other than optimum load impedance for the negative impedance device. Also, in prior art microwave oscillators it is generally impossible to raise the Q through a redesign of the various circuit parameters without seriously affecting the power output or optimum load impedance. In most prior art microwave oscillators all of these three features interact and changing one of them adversely affects the other two.
Two typical prior art devices are disclosed in U.S. Pat. Nos. 3,628,171, entitled "Microwave Power Combining Oscillator Circuits," issued Dec. 14, 1971, and 3,931,587, entitled "Microwave Power Accumulator," issued Jan. 6, 1976. Both of these devices use wave guide as a resonant cavity for accumulating or combining power. Becuase of the wave guide resonant cavity, these structures are larger and more expensive. Also, in U.S. Pat. No. 3,931,587, the power must be removed by means of a central probe. In addition it is difficult to obtain tight coupling between the transmission lines and the wave guide resonant cavity so that transformers are required.